1. Field of the Invention
The present invention relates to a mobile communication system, particularly to a mobile communication system having a function of detecting a position of a mobile station.
2. Description of the Related Art
With spread of a mobile communication system utilizing wireless communication, there has been desired development of a mobile communication system capable of detecting a current position of a mobile station changing every moment such as a portable telephone or a pager and dealing with a diversified communication environment of the mobile station while establishing a stable communication state based on information of detecting thereof.
As methods of detecting the current position of a mobile station, there have been known methods of detecting a position of a mobile station in a mobile communication system of a CDMA (Code Division Multiple Access) system disclosed in Japanese Patent Kokai No. 7-231473 and Japanese Patent Kokai No. 11-308658.
According to the former method of detecting a position of a mobile station, a mobile station detects respective reception electric field intensities of radio waves coming from a plurality of base stations and a position of the mobile station is predicted based on the detected reception electric field intensities.
According to the latter method of detecting a position of a mobile station, a mobile station detects respective reference signals transmitted from a plurality of base stations in synchronism with each other and predicts a position of the mobile station based on phase differences of the reference signals.
However, according to the method of detecting a position of a mobile station disclosed in Japanese Patent Kokai No. 7-231473, the distances from the mobile station to the respective base stations cannot be detected with high accuracy and therefore, there poses such problem that it is difficult to predict the position of the mobile station with high accuracy, when there is not a significant difference in respective distances from the mobile station to the plurality of base stations.
Further, according to the method of detecting a position of a mobile station disclosed in Japanese Patent Kokai No. 11-308658, there poses the problem that it is difficult to predict the position of the mobile station with high accuracy, when there are not direct waves from the plurality of base stations to the mobile station, the distances from the respective base stations cannot be detected with high accuracy.